There are numerous methods and devices available for the detection of how different species interact. In the field of biochemistry, one common measurement is to determine how strong an antibody interacts with an antigen, so as to better understand immunological processes. In drug discovery, similar measurements are conducted to determine how strong a small molecule is interacting with a disease-related target, so as to better understand if the small molecule is worth further investigations as a potential drug.
One particular type of method and device for measuring the interaction of different species is disclosed in WO2005080967, which is incorporated by reference herein. Such a device, currently commercially available under the trade name LigandTracer, is capable of measuring interactions between a range of species. In WO2005080967, it is described that the device can measure how a radiolabeled protein interacts with living adherent cells. In the scientific literature there is currently examples of such a device monitoring interactions between virus in suspension and adherent cells, between suspension cells and adherent cells, between small molecules and adherent cells, between proteins in solution and proteins adsorbed to magnetic beads which in turn are anchored through a permanent magnet, and the dissociation of chemicals from solid nanoparticles, to mention a few illustrative examples.
Generally, the device according to WO2005080967 is a device suitable for detecting interactions between species attached to or positioned on a solid support (targets) and species in a liquid (ligands), when said solid support and said liquid are brought into contact. On the solid support, a first species (target) can be attached in one or more non-overlapping defined areas. There is a detector capable of detecting an interaction between said species attached to the solid support, and said species contained in said liquid. The device is characterized by a mechanism adapted for temporarily reducing, in a defined area of said solid support, the amount of liquid with which said support is brought into contact in the course of a detection; and at least one of the defined areas do not have a species of interest attached, so as to form a reference area for the detection. Preferably the solid support as described in WO2005080967 is an essentially flat dish capable of holding a liquid confined within its boundaries, such as a Petri dish, although any other kind of receptacle or vessel capable of confining liquid is possible. The detector could for example be a scintillation detector or a fluorescence detector, although many other types of detectors are possible. The device is connected to a computer for synchronizing detector output with solid support orientation. The key feature in the invention in WO2005080967 is that the amount of liquid covering the defined portion of the support is temporarily reduced prior to performing said measurement. The temporary reduction of liquid comprises a reduction of the amount of liquid near at least one of said defined areas without changing the total amount of liquid in contact with said solid support. A reference measurement is performed on a different portion of the solid support where no interaction takes place, said portion defining a reference area. Suitably, a difference between target and reference measurements is calculated. The sequence of steps of exposing, measuring and reducing the amount of liquid is preferably repeated approximately once every minute, and the concentration of said ligand is increased by a finite amount before said sequence of steps is repeated.
One method for achieving the reduction of the amount of liquid is by orienting the support at an angle that deviates from the horizontal to provide an elevated part and a lower part of said support, such that the elevated part will be covered by less liquid than the lower part, and wherein the support is rotated at a predetermined speed. An alternative method for achieving the reduction of the amount of liquid is achieved by tilting a solid support back and forth.
The solid support as described WO2005080967 in is typically a container. In this container two or more defined areas are present. One liquid put in the container and said liquid contacts all defined areas. At least one defined area is always reserved for reference purposes. The attachment of target on defined areas can be performed in a variety of ways. Cells could be grown directly on a defined area. The defined areas could be coated with a protein known to enhance attachment of cells. The defined areas could be coated with a protein known to bind a specific molecule which is used for attachment of the target. One such protein is streptavidin which binds biotin strongly. A biotinylated target (e.g. biotinylated DNA) could then be conveniently attached as target to the defined area. The surface of the defined areas could be chemically modified to make possible covalent attachment of a target. Passive adsorption of target directly onto the defined area is also possible. The surface of the defined areas is not necessarily solid and flat. Porous surfaces or surfaces with biopolymers attached (e.g. polyethylene glycol or dextran) could be advantageous due to increased target density making a higher signal possible.
In “Biochemical and Biophysical Research Communications 428 (2012) 74-79” there is disclosed that a permanent magnet can be placed under a defined area to anchor magnetic particles in the defined area.
The current LigandTracer® device is designed for attaching one or more species (one or more targets) to a solid support and to keep the other species (or ligand) in solution or suspension. Currently, regular Petri dishes are used as solid support.